Comparison of raw and roasted narbon beans ( Vicia narbonensis) on performance and meat sensory attributes of lambs fed a roughage-based diet

Abstract

This study examined the effect of raw and roasted narbon bean ( Vicia narbonensis) in a roughage-based diet on growth performance and meat sensory attributes of sheep. Roasting was examined to determine whether it improved protein utilisation. Lambs ([Border Leicester×Merino]×Poll Dorset; 6 months old, mean liveweight of 34.9 kg) were allocated to three treatments ( n=8 per treatment): Nil, lucerne and oaten chaff; raw WNB (chaff plus raw whole narbon bean); and roasted WNB (chaff plus whole narbon bean roasted at 150°C for 45 min). Raw and roasted narbon bean supplied 56% of total protein (approximately 15% DM) and were fed for a period of 8 weeks. Growth performance was evaluated over 6 weeks followed by a 7 day nitrogen balance measurement in five lambs from each treatment. Remaining three lambs were maintained on their treatment diets and all lambs were slaughtered at the end of the nitrogen balance study after blood samples were taken. For Nil, raw and roasted WNB ADG was 84.3, 158.1 and 171.6 g per day; FCE 16.5, 7.7, 7.2 kg/kg DM and nitrogen retained 6.4, 6.9, and 8.3 g per day, respectively. At slaughter, HCW, was 18.5, 21.4, 22.3 kg; fat depth 12.6, 17.9, 17.6 mm, and dressing percentage 45.9, 49.9, and 51.4% for Nil, raw and roasted WNB, respectively. There was no significant difference between raw and roasted WNB for any performance trait. In contrast, all performance traits except for nitrogen retained were significantly ( P<0.05) different between Nil and raw and roasted WNB. Dry matter and organic matter (average 1233 and 1157 g per day, respectively) intakes were similar across treatments but there was a significant ( P<0.05) increase in dry matter (raw, 11.4% and roasted WNB, 11.9%) and organic matter digestibility (roasted WNB, 10.9%) compared with Nil. Changes in metabolite concentrations were variable. However, change in PUN concentration at 3 h after feeding was significantly different ( P<0.05) between Nil (1.39 mmol/l) and roasted WNB (0.29 mmol/l) indicating a reduction in level of rumen-degradable protein in roasted WNB. There were no significant differences in ‘aroma liking’, ‘flavour liking’, ‘juiciness’, ‘overall acceptability’ and ‘tenderness’ of meat between treatments. However, compared with Nil ‘aroma strength’ and ‘flavour strength’ was significantly higher ( P<0.05) in roasted WNB. We conclude that inclusion of raw or roasted narbon beans in a roughage-based diet improved FCE in young sheep through an increase in ADG and has no detrimental effect on meat sensory properties of lamb. Improvement in performance was achieved through an increase in total tract digestibility and hence an increase in ME intake. Roasting narbon beans provided no additional benefit for lamb performance.